The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
I am aware of statistical tests for white noise in a real signal (Box-Pierce, Ljung-Box tests) and red noise (Percival test) but am unaware of any statistical tests for pink noise in a signal and cannot find any literature on this, only properties of pink noise and the generation of pink noise. Does anyone know of any? — Preceding unsigned comment added by 211.31.25.66 (talk) 07:48, 31 October 2013 (UTC)[reply]
Articles related to Flicker noise have detection and elimination techniques. Suppressing flicker noise below the thermal noise floor is generally the goal. Double correlated sampling and chopper stabilization are techniques to move the flicker noise below thermal noise. detection is basically all 1/f noise is pink noise. --DHeyward (talk) 08:11, 31 October 2013 (UTC)[reply]
I think it's important to point out the distinction between pink noise and flicker noise, which our articles don't make clear. Pink noise is any noise with a 1/f (3 dB per octave) spectral density. Flicker noise is a type of pink noise produced in electronic devices. The two terms aren't synonymous. Tevildo (talk) 22:14, 31 October 2013 (UTC)[reply]
Flicker noise does from the description seem to resemble shoot noise but where every single electron contributes and thus it looks different but have the same base? Electron9 (talk) 23:39, 31 October 2013 (UTC)[reply]
It is indeed important to realsise that there is a very important difference between flicker noise (also known as 1/f noise) (f for frequency) and pink noise. The Wikipedia articles on flicker noise and pink noise are all mixed up - the authors have been confused on the meaning of "1/f".
Flicker noise arises in vacuum tube cathodes, junctions between thin metal films, and junctions between metals and semiconductors, has a power spectrum that drops 6 db for each octave increase in frequency, and rises in proportion to the square of the DC current thru the junction. Saying that it drops 6 dB for each octave increase in frequency is of course the same as saying flicker noise voltage is proportional to 1 / frequency. Since power is proportional to voltage squared, power drops 4:1 for each 2:1 increase in frequency.
Pink noise is white noise that has been filtered to produce a power spectrum that drops 3 dB (ie power halves) for each octave increase in frequency. When expresed as a voltage, pink noise halves for each 4:1 increase in frequency. Because of this, pink noise cannot be produced by a capacitor shunting a noise current source. In analogue circuits, pink noise is produced by a complex network of capacitors and resistors that approximates an impedance proportional to (1/f)1/2, not 1/f.
One way to prove out pink noise is to inverse filter it (i.e., use an A = k.f1/2 filter) back to white noise in a finite bandwidth and then apply the usual tests for band limited white noise.
Note: Those of us old enough to have worked with vacuum tube operational amplifiers, and those of us who are old enough to have listened to the amplified Low frequency noise from the early junction transistors (eg OC71, AC125, Japanese HJ15, etc) know why popcorn noise is called popcorn noise. And we know it is random, but it sure doesn't sound like pink noise or filtered thermal noise.
A classic textbook that covers white, coloured, and popcorn noise is: Electrical Noise by W R Bennet, McGraw Hill 1960. An oldie but a goodie. Poporn noise discussion starts on Page 87.
I had a quick search online for a popcorn noise sample, without success. That's not surprising, as popcorn noise has long been just about a non-problem. It was a problem with the early (1950's) germanium junction transistors. Some were worse than others - you could buy more than you needed and select on test the good ones. To the best of my knowlege, no physicist has figured out a workable theory for popcorn noise yet, but manufacturers have long worked out from experience factory processing methods to all but eliminate it - at least to the degree that shot noise predominates. When you amplify the noise from a good bipolar transistor, it sounds just like white noise (which is of thermal origin - the random movement of charge carriers). It sounds as in "hissssssss.....". It you filter white noise to make pink noise, by comparison it sounds more of an "ahhggrrrrrr....". If you then band limit it to say 0 to 300 Hz, it then sounds like LP record rumble. If you amplify the noise from the early germanium junction transistors (OC71 & the like), and band limit it to the same 0 to 300 Hz to get rid of the masking shot noise, it sounds vaguely like popcorn popping in those big display poppers movie theaters have. It sort of comes and goes a bit like the noise of popping popcorn does.
Incidentally, another name for popcorn noise is burst noise. Wikipedia has a short article entitled Burst Noise, apparently written without knowlege of the popcorn / 1/f article (or was it vice versa?)
Certainly not me. If I was to set out to correct all the errors in Wikipedia articles that come within scope of my chosen professional field, I'd be doing it full time for years - only to have some peanut revert it again. Certainly not me, not until Wikipeia institutes a system of moderators at at any rate. 120.145.135.143 (talk) 12:07, 1 November 2013 (UTC)[reply]
One way to deal with it is to produce a "good version". When peanut lifeforms come around and mess it up other people will find the good version in the change history. Usually the coherent content and solid sources is a sign of good a article. Electron9 (talk) 19:52, 1 November 2013 (UTC)[reply]
Agriculture and global food supply
Can you tell me what the current amount of staple foods needed for the world supply is? I want to know the amount of food produced for at least 3 staples and the total world population of those 3 staples.--131.96.121.122 (talk) 13:53, 31 October 2013 (UTC)[reply]
Is meat one staple, grain another staple, and fruits still another staple?
Actually, having looked at the article, I think it fails to define the concept strictly enough. As I understand it, a true "staple" is a single food from which you get the overwhelming majority of your calories, say 80%, day in and day out. That's why there can never be more than one, and for most people, zero. --Trovatore (talk) 17:43, 1 November 2013 (UTC)[reply]
This will trap a layer of air between the clothes, and air has a very low thermal conductivity coefficient. So, what then happens is that the same amount of heat that your body produces must still escape via your clothes, but this heat will escape from the top layer of your clothes, So at that top layer the temperature will be the same (because heat transfer depends on the temperature difference and the heat transfer between the top layer and the air will be the same). Then the hat transfer from your body to that top layer must also be the same in bith cases, but nowwith more air trapped between the top layer and your body, the tamperature difference must be larger, so the temperature at your skin will be larger. Count Iblis (talk) 14:56, 31 October 2013 (UTC)[reply]
An air layer is part of the answer, but two layers of the same material also cuts in half the heat transferred by conduction through the fabric, and also decreases the flow of cold wind if the fabric is porous enough to allow any air current. Edison (talk) 18:55, 31 October 2013 (UTC)[reply]
Layers also provide another advantage: It's important to prevent sweat from building up, which can then make you very cold and uncomfortable later. With layers, you can add or remove layers as needed, to keep comfortable. If you had a single, thick item of clothing, you would lose this flexibility. StuRat (talk) 16:49, 31 October 2013 (UTC)[reply]
This is probably clear, but just in case: Clothing doesn't produce any warmth, it is only your body that produces warmth. Clothes only reduce the heat loss of the body. You can wrap a stone in as many layers as you wish and it will not warm up.86.179.30.226 (talk) 22:41, 31 October 2013 (UTC)[reply]
I should add that the reason sweaty clothes are so bad is that sweat greatly increases the thermal conductivity of the material, allowing body heat to escape much more quickly. StuRat (talk) 06:11, 3 November 2013 (UTC)[reply]
RPG-29
I have a curiosity about RPG-29 rocket: in its technical description is said that it could penetrate 750 mm of RHA (Rolled homogenous armour) or 1500 mm of reinforced concrete. This sound to me very strange: the reinforced concrete has a tensile strength of 12-15 megapascal and the RHA of 1000-1200 megapascal (80 times higher). How it's possible so low difference beetwen the two penetration? Isn't maybe the data for RHA overstimed or there is any other reason? 80.116.228.89 (talk) 17:37, 31 October 2013 (UTC)[reply]
An RPG uses a shaped charge. The liner of the charge is compressed into a narrow jet of metal moving at speeds up to 14 km/s. At those speeds, the strength of the armor plays a minor role, it's mainly the density or weight that determines how far the charge penetrates, that's why some tanks use depleted uranium in their armor. Ssscienccce (talk) 18:26, 31 October 2013 (UTC)[reply]
See also composite armour, that mentions that fused silica glass had a higher stopping power than steel (not sure that can be explained by density). To defend against hollow (shaped) charges, explosive reactive armor has been developed: an explosion moves part of the armor while the jet of the shaped charge is penetrating, disrupting the shape of the jet and diminishing the penetrating depth. To defeat reactive armor, the RPG-29 and other HEAT rockets use two shaped charges, the first will trigger the explosive charge in the armor, the second strikes milliseconds later, when the armor isn't "reactive". Ssscienccce (talk) 19:13, 31 October 2013 (UTC)[reply]
'Real world length contraction' moved to archives. Why?
I'm new here... wondering why discussion of my question "'Real World' Length Contraction" was deleted from the current menu and moved to the archives, while, for instance the "vomiting while pregnant" question and others remains on the up-front menu. Wherever I raise the question of a variously contracted Earth diameter, or contracted distances between stars... depending on all varieties of relativistic frames, I am either called a crank (and banned from science forums) or told that challenging mainstream length contraction is inappropriate... or the topic is hidden in the backwaters, like the archives here. Will someone here please explain why my question was brushed aside as above with no answer? Thanks — Preceding unsigned comment added by 63.155.141.178 (talk) 17:58, 31 October 2013 (UTC)[reply]
If there's more you feel needs to be explored, feel free to open a new question along those lines. Ideally, don't just ask the same question (unless, say, no one responded at all), but focus on what you feel was not addressed. --Trovatore (talk) 18:16, 31 October 2013 (UTC)[reply]
Thanks. The question was left hanging at the challenge of a shrinking Earth diameter, depending on the velocity and direction of relativistic frames observing it. The muon question was also left unanswered. I'll open a new question on those cases of supposed contraction specifically.
The point is that you come over as quite hostile. You're essentially saying "I don't believe in Special Relativity - it's impossible" - which is not asking us a question. In fact, you're entirely wrong. Special relativity is true - it's one of the better tested scientific theories - and much of what happens in the universe can only be explained by it being true. People have gone so far as to measure the ticking of the clocks on actual, for real spacecraft to see if time is slowed for them - and it is. If you own a GPS unit - you may be surprised to know that there is software inside that little box that has to compensate for both special and general relativity in calculating where you are in the world. This stuff really isn't up for debate.
So we're telling you the answer - "The Truth". It's OK if you don't fully understand it - by all means, ask for clarification. But issuing "challenges" and being generally combative is hostile to our volunteer staff, who's mission here is to tell you the truth and explain it if you don't understand. We're not here to disprove or challenge whatever wonky ideas you may have of your own. If you wish to dismiss all of mainstream science on this point and ignore what 100% of the respondents here are telling you, that's fine - go away and be flat out wrong someplace else. But please don't argue with us. We're telling you the truth as researched most carefully by hundreds of people who were all a lot smarter than any of us here!
Subjects like relativity and quantum theory are strongly contrary to "common sense" - but that's not because they're wrong - it's because we humans have evolved in a world where nothing much moves anywhere near to the speed of light (except light) and all of the objects we deal with routinely are bigger by far than an atom. The "common sense" that we evolved as stone-age hunter-gatherers on the African plains is pretty much useless for explaining what goes on in realms that it did not evolve to handle...so we find it hard to get our heads around the reality of the universe at these crazy speeds and scales. I forget who said it, but: It's not natures' duty to be understandable by mankind.
Perhaps you'd do our volunteers the kindness of toning down your rhetoric - and rather than telling us that this is all wrong and impossible (which it's definitely not), confine yourself to politely requesting clarifications for the parts that you don't understand. Do that, and things will progress more smoothly.
I didn't read all that, but you apparently missed his question, the OP asked for an explanation or the underlying mechanisms regarding length contractions. Not that hard is it? And of course, "100% of the respondents here are telling you" is not accurate (reread the thread). --Modocc (talk) 00:17, 1 November 2013 (UTC)[reply]
Should we run an experiment with a plane and measure the Earth's various contractions while dog-fighting, we could build a huge database and subject it to supercomputers and produce funky maps, but that would not necessarily change how the data is processed. However, I'm a scientific realist, because our science is evolving (for instance, compare how messed up ancient land maps used to be compared with today's detailed maps) and it's going to take some effort to progress further. Like Steve said, it is OK to ask for clarification on relativity, but this isn't the appropriate place for debate (see the policy guidelines above). -Modocc (talk) 01:40, 1 November 2013 (UTC)[reply]
Contracted Earth diameter and atmosphere depth
My "real world length contraction" question was moved to the archives (after the 5 day limit, I'm told... but doesn't seem to apply to other topics), so here are the unanswered challenges from that exchange:
If a relativistic frame (future ship or whatever) approaches Earth in the direction of its axis at .866c, special relativity (SR) says that it will measure the polar diameter to be about 4000 miles. Then if it turns around and approaches at the same velocity in the direction of the equatorial diameter, that will now be measured as 4000 miles, and the polar diameter will have restored to its proper length just under 8000 miles. SR insists that all frames are equally valid, so then Earth must "morph" with every possible velocity and direction from which it could (relativistically) be observed. True of false?
Muons traveling through our atmosphere have higher velocities than lab-accelerated muons, so they decay more slowly ("live longer") and therefore travel further than lab muons, so they can reach Earth's surface. SR claims that the depth/thickness of the atmosphere contracts "for those muons." But the atmosphere remains about 1000 km all around Earth at all times, not contracted by what incoming muons would "observe." Different observations can not change physical objects or distances. SR claims that it does. SR advocates now have another 5 days to reply to this challenge. — Preceding unsigned comment added by 63.155.141.178 (talk) 18:51, 31 October 2013 (UTC)[reply]
SR says that the squared invariant distance between two points in space-time (x,y,z,t) and (x',y',z',t') is
s^2 = (t-t')^2 - [(x-x')^2 + (y-y')^2 + (z-z')^2]
where the time and the positions are measured in the same units (so the speed of light, is set equal to 1). So, SR disputes the validity of Pythagoras' formula and it disputes that time intervals are invariant. Count Iblis (talk) 19:32, 31 October 2013 (UTC)[reply]
I don't see your problem here. Relativity says that sizes, masses, rate of passage of time and a bunch of other things depend on the frame of reference of the observer. In your example, people approaching the earth from different directions and speeds would indeed see the earth as having different sizes and shapes simultaneously. The idea that two people perceive things differently because they are moving at different speeds and directions should come as no surprise to you.
It's not quite a correct analogy - but consider the doppler effect for sound.
There is a person driving a fast car along a straight road and a person standing still at the side of the road. As he's driving along, the first guy leans on the horn and hears a sound of constant pitch as he passes the guy who's standing still. But the guy standing on the side of the road hears a higher pitched sound as the car approaches him and a lower pitched sound as it passes him and heads off into the distance. Ask the two people what pitch the horn had and they'll disagree. The horn doesn't have to have two pitches simultaneously - it's just that the frame of reference for the two observers is different. Position 100 people at different points along the road, all moving at different speeds and you'll get 100 different perceptions of the exact pitch of the car horn.
CAVEAT: This isn't actually a very good analogy because sound exhibits doppler differently from the way light does - but the point is that it's OK that an object can simultaneously be perceived as being many different sizes, masses, etc by different observers.
As I said before, you have to read (and completely understand) things like the Ladder paradox. In that example, a fast-moving 20' ladder fits into a 10' building - from the point of view of an observer standing next to the building - and the 20' ladder moves through the 5' building from the point of view of an observer riding on the ladder. This is entirely non-contradictory - but it is confusing as all hell for people who aren't comfortable with special relativity.
So the answer to your first question is that the earth doesn't "morph" - it simply "is" a whole bunch of different sizes (etc) depending on the frame of reference of the observer.
Your description of what happens with Muons is correct. From our point of view, they are moving ungodly fast, so time for them has slowed down - so they make it through the atmosphere without decaying. From the muons' point of view, time is ticking along normally - but the earth (and it's atmosphere) has contracted to a nearly flat circle and the atmosphere is so thin that it can make it through easily. This is not contradictory - it's an entirely consistent story - and the outcome (that the muon makes it through the atmosphere) is perfectly correct from both viewpoints.
You boldly assert that "Different observations can not change physical objects or distances." - but you are quite wrong. That is exactly what does happen. Consider the behavior of muons to be proof of that. There have been numerous other experiments that demonstrate this kind of thing. Special relativity is a proven fact - weird though it seems. You really can fit a 20' ladder into a 10' building if you move it fast enough...but if you're sitting on the ladder, things seem VERY different.
But think back to my (technically, rather bad) car horn analogy. Different observations of the car horn did change the frequency at which the various observers heard the sound. This is just like that (although the analogy is only perfect for lightwaves - not sound).
If I might indulge in a bit of devil's advocacy - the statement "different observations cannot change physical objects" is correct (in this context, although we might get to the Copenhagen Interpretation soon). Different observations change the values of measured times and distances for a given (unchanging) physical object. The object doesn't change, although its length does. Tevildo (talk) 21:23, 31 October 2013 (UTC)[reply]
Yes...we should perhaps think of the "rest length" of an object (like it's "rest mass") as being a constant that doesn't change, and that all practical measurements of the object are a combination of the rest-length and a scaling factor that depends on relative motion. Splitting the length into those two parts resolves the confusion. The object's rest-length is an unchanging property of the object itself but it's modified by a factor that is observer-dependent. However, the key point here is that this second factor isn't like an optical illusion or seeing something in a distorted mirror. The point of the Ladder paradox is that a fast-moving object doesn't just look smaller - it will actually fit into a smaller space...from the perspective of some observers.
I think it's resolved if you use the unchanging speed of light as the measurement. A 1 meter bar measured with a 1000nm laser is 1 million wavelengths long. I believe it's always 1 million wavelengths long. That fact that an observer will disagree on the wavelength of the laser, but not the speed of light or the number of wavelengths measured by the comoving laser is the invariant physical property. --DHeyward (talk) 09:50, 1 November 2013 (UTC)[reply]
Your "challenge" is like saying that the rules of perspective require objects to grow and shrink. The only difference between that case and this one is that there aren't a bunch of dumb popular books telling you that perspective means that the size of objects is "relative to the observer" and that that has profound philosophical implications. Ignore the second-rate philosophy and you'll be fine -- BenRG (talk) 21:39, 31 October 2013 (UTC)[reply]
I like that analogy...but we have to be a little careful though. The moon seems like it would fit into a matchbox because of perspective - but we know that it's not "really" that small and that it won't fit into such a small space. With Special Relativity, if the moon were moving so fast that it appeared to be that small, it really would fit into a matchbox. SteveBaker (talk) 21:49, 31 October 2013 (UTC)[reply]
Well, no, for a couple of reasons. First of all, length contraction is only in the direction of motion, so you'd need a Moon-sized matchbox in the other two directions. Then, yes, in the matchbox's frame of reference, you could (very briefly!) have the Moon contained within the top and bottom of the matchbox, say a centimeter apart, but only because you don't agree with the Moon about simultaneity. You'd have to let the Moon in, close the box (that might involve moving the top faster than the speed of light, but whatevs), then bask in the satisfaction that the Moon is inside the box before it obliterates the other side. From the point of view of a lunar observer, the events happen in a different order. --Trovatore (talk) 21:55, 31 October 2013 (UTC)[reply]
Yeah - sorry, you're right about the contraction being only in one direction - you couldn't get the moon into a matchbox like that - but a pole that's the same diameter as the moon would...and the distinction between that and perspective is significant. SteveBaker (talk) 03:48, 1 November 2013 (UTC)[reply]
Only I know of no events that have been measured to have occurred in reversed order due to frame differences. Also, BenRG perspective analogy and Steve's admission objects don't "change" admits to what? Changes in perspective which means what? Apparent change, in a way similar to the way stars go flying about when I turn around. --Modocc (talk) 02:18, 1 November 2013 (UTC)[reply]
No! You are completely wrong. The idea that you literally can fit a 20' ladder into a 10' building by moving it fast enough (again, please read ladder paradox) means that this is a very different thing than perspective and things moving in your field of view when you move your head. This is a completely physical dimension change. SteveBaker (talk) 03:48, 1 November 2013 (UTC)[reply]
No! You cannot fit a 20' ladder in a 10' room, since fit means "store within unmoving", not "pass through at close to the speed of light". μηδείς (talk) 03:56, 1 November 2013 (UTC)[reply]
No? Think about the implications Steve, if that were true then an electron accelerated at our labs (or something bigger in the future) could cause the Earth or our Sun (or some distant star) to be made so thin that it will fit in gigantic envelope. -Modocc (talk) 03:54, 1 November 2013 (UTC)[reply]
The implications have been thought of before by some very smart people. See ladder paradox. The sun very well can fit in a very wide envelope, in a certain reference frame, and only briefly. Standing in another reference frame the sun would burst out the back of the envelope and only a small portion would be inside at any one time. There is nothing about this that is either contradictory or which breaks the laws of physics - it's simply a matter a perspective, and its very very weird. Someguy1221 (talk) 04:02, 1 November 2013 (UTC)[reply]
More importantly, physical changes only happen with the speed of light, thus the fact that I drove instead of walked to the store yesterday does not mean our neighboring galaxies shrank a tad more during my faster trip than on the previous day even though my frame did change. -Modocc (talk) 04:18, 1 November 2013 (UTC)[reply]
The comment on proper length above reminds me of a question: rather than saying sqrt(x^2+y^2+z^2-c^2t^2), could we define time as an imaginary number t' = ict, so you'd have sqrt(x^2+y^2+z^2+t'^2)? Since this is obvious I imagine there's some reason against it... Wnt (talk) 03:51, 1 November 2013 (UTC)[reply]
That actually was a popular approach for some time; it went out of fashion somewhere in the latter half of the 20th century. The problem with it is, it's a bit too cute; it obscures the difference between a true metric and a pseudometric, which is a real difference. If proper time were a true metric, then you couldn't have two distinct (event) points that have interval 0 between them — but you can. --Trovatore (talk) 04:16, 1 November 2013 (UTC)[reply]
Hmmm, can you explain this about the two event points? I see it is mentioned in metric (mathematics) but I'm totally not getting how spacetime isn't a metric (or in general, what "d" means in this context). Wnt (talk) 07:08, 1 November 2013 (UTC)[reply]
The metric defines a norm on the vector space and this should then satisfy all the axioms for a norm. One of the axioms is that ||x|| = 0 if and only if x = 0. Now imaginary time is used in quantum field theory, to get nicer behaved path integrals, the amplitude of a process is given as a path integral over exp(i Action of field configuration), and you can change the integrand to this to exp(- Euclidian Action of field configuration). As explained here in the "Alternative" to the WKB approximation, you see that the imaginary term becomes a real term, but the potential changes sign. So, instead of having to consider a tunneling through a potential barrier, the problem is now a particle propagating from one hil to another throug a valley, and then it is immediately clear what the dominat contribution to the path integral is. All you then have to do is to transform the asnwer back from Euclidian time to ordinary time. Count Iblis (talk) 18:40, 1 November 2013 (UTC)[reply]
Actually, I believe the proposition of SR is that the only invariant physical property is the speed of light is the same in all frames of reference, energy of light is inversely proportional to wavelength and energy is conserved in all frames of reference. This is the fundamental property that "distorts" lengths, time, and mass. Say you have a laser in spaceship that is moving towards earth in your spaceship. The wavelength in that frame is 440nm. Couple that with the velocity of light and you can measure distance. But another observer in a different frame measures the laser and has the same speed of light. The kinetic energy of motion changes the wavelength of light, though, not the speed. This is counter-intuitive to our normal experience that kinetic energy increases velocity. Let's say the "at rest" observer measures the laser wavelength at 220nm as it moves toward him. If you treat the wavelength of the laser as unit length dimension, how many wavelengths are the two objects apart? If I say the distance between the two objects is 1,000,000 wavelengths because the speed of light is fixed, suddenly the measured distance changes depending on the observer relative velocity. Not only that, but if earth had the same 440nm laser pointed at the spaceship, the spaceship would see a 220nm laser. The consequences of measuring with a fixed speed of light, conservation of energy and the energy of light being inversely proportional to wavelength, gives rise to all the relative weirdness. --DHeyward (talk) 09:34, 1 November 2013 (UTC)[reply]
We actually have an article on the postulates of special relativity. As originally formed, Einstein only assumed that the laws of physics (specifically Maxwell's equations) are equally valid in all reference frames, and the speed of light is invariant between reference frames. This is why what the OP is asking for, a mechanism, cannot be provided. As you say, length contraction and all the other weird phenomena that are observable thanks to special relativity are direct consequences of these postulates, and not any complicated physical mechanisms. As that article mentions, there are also other derivations of special relativity that do not require any assumptions about light, but yield the same conclusions (in addition to concluding that the speed of light is invariant). Someguy1221 (talk) 10:09, 1 November 2013 (UTC)[reply]
DHeyward and Someguy are correct. In addition, with respect to proof, one also can ignore SR postulates and merely point to the results of direct measurement! So there is no "need" for the postulates in that sense. ;-) So people can be pretty stubborn about this. In addition, unwavering standards are important, thus with the invariant light-speed yardstick relativists have had a substantial degree of success with this, sort of. Consider how we go about measuring the density of gold precisely, one needs pure gold that isn't being periodically contaminated. Likewise, suppose we measure the height of students with a wooden doorframe, and the students' heights vary slightly with time. Suppose too that we don't know what the cause is, but any theorist with this data can certainly conclude that the students' heights are changing periodically simply because of the data and his maths backs him up. He has solid, rock-hard data correlating the changes to something, but he has no idea why, but claims that since his proposed model is correct thus far, it will continue to be (even though he is predicting time reversals too). That's fine, but if someone is predicting measurable time reversals, I'd tell the door frame theorist to back up and rethink the problem and their assumptions from scratch, by studying the dynamics of that door. -Modocc (talk) 14:55, 1 November 2013 (UTC)[reply]
My opening paragraphs have not been addressed. The "challenge" is that obviously Earth neither changes diameter lengths (it is a semi-solid/rigid body, and there is no physics explaining physical contraction)... nor does it "have" and infinite number of diameters at the same time as according to all possible frames measuring from all possible speeds and directions of travel. Neither does the atmosphere change in depth (etc.) as a result of the velocity of incoming muons. (See my second opening paragraph.) The philosophical basis implicit in such claims is the idealism (as per Einstein) that there is no "real world" independent of observation. This has come to be expressed in SR's dictum that "there are no preferred frames of reference"... that "all are equally valid," so Earth's diameter "depends on how you look at it," in common vernacular. Realism, on the other hand, "realizes" that the world/cosmos exists "as is" (as formed and naturally changing according to the laws of physics) independent of changes in how it (any given object or distance) might be observed (from relativistic frames in this case.) My contribution to science as a professor of the philosophy of science (retired) has been to contrast Einstein's idealism (that reality depends on observation) with realism (that the world exists and has its intrinsic properties in and of itself independent of observations/measurements.) I ask again that this issue be addressed as a clarification of whether physical objects/distances shrink as a result of various observations, and if so, by what physics. I have been prompted to sign my posts. I was repeatedly insulted as a crackpot and told that my contributions to "disambiguate" length contraction were inappropriate in the editing discussions of the LC section, so I came to the reference desk, as suggested, with this perspective. Again, please address my opening paragraphs. LCcritic (talk) 18:35, 1 November 2013 (UTC)[reply]
The line between physics and metaphysics has always been arbitary, but special relativity is comfortably on the scientific side. I'm afraid your statement "Earth neither changes diameter lengths... nor does it have [an] infinite number of diameters" is just wrong - it is not consistent with repeatable observations that can be performed in the real, physical world. The Earth's measured diameter _does_ change, depending on the relative movement of the Earth and the observer. You may deny the truth of this statement, but the Universe (and not just we humble RD editors) doesn't agree with you. A discussion of what "true" and "the physical world" and "reality" mean are within the realms of metaphysics, and more appropriate for the Humanities desk, but, whatever the words mean, the Earth's diameter still shrinks. Eppur si muove. Tevildo (talk) 19:04, 1 November 2013 (UTC)[reply]
Special relativity is physics, but it's questionable whether special relativity, per se, has an opinion on whether the Earth "really" shrinks. I'd say that's a bit outside its remit.
The Earth's diameter will be different in the coordinate system of an observer moving relative to the Earth, but, you know, it's just a coordinate system. You can come up with all sorts of silly coordinate systems. The only difference is that it's a coordinate system that's especially convenient for the moving observer; it has some special properties, and these can indeed be confirmed by experiment. But whether those properties equate to a "real" shrinkage is a matter of interpretation, not physics in the strict sense. --Trovatore (talk) 20:54, 1 November 2013 (UTC)[reply]
The diameter of the Earth measured by the moving observer _is_ less than the diameter measured by the stationary observer. That's physics. Is this a "real" shrinkage? That's metaphysics, but only as regards the meaning of the word "real". The diameter is smaller, whatever we say about it. Tevildo (talk) 21:08, 1 November 2013 (UTC)[reply]
But the "diameter" is just the difference between two coordinates in a coordinate system, and coordinate systems are essentially arbitrary. The only thing that connects the coordinate system used by the observer to the phrase "measured by the observer" is certain coherency properties that it has for that observer. The connection between that and the question of "real shrinkage" is a bit tenuous. --Trovatore (talk) 21:16, 1 November 2013 (UTC)[reply]
So, is there a "real diameter", which is not the difference between two sets of coordinates? If so, how is it defined? How can it be measured? Assuming the Lorentz tranform does not apply to this measurement, in what sense is it a "length"? Tevildo (talk) 21:31, 1 November 2013 (UTC)[reply]
I didn't say there was a "real diameter". If there is no "real diameter", then there's also no "real shrinkage", n'est-ce pas? But what I think LCcritic is getting at is, the atoms that make up the Earth don't care about the coordinate system of some observer moving relative to them; they just keep their appointed distances from one another, in the coordinate systems convenient for them. The sum of those distances makes up the "diameter of the Earth" in any ordinary sense, irrespective of what observers might do.
I think this is really kind of a good point that is being obscured in this discussion. If I speed up, does it have any effect physical effect on the Earth itself? No, of course not, and I don't think anyone ever really said it did, which is why the point probably doesn't resonate so much with a lot of people who have already internalized SR. They already know that; it seems like a strawman. But we should recognize that it is a point of confusion. --Trovatore (talk) 21:41, 1 November 2013 (UTC)[reply]
Yes, I see your point, the presence of the moving observer doesn't affect the stationary observer's measurements, although saying that the Earth shrinks might sound as though it does. My point is that the moving observer's measurements are equally as "real" as the stationary observer's. The cosmic ray muons mentioned earlier really do have a longer lifetime than the laboratory muons, and the atmosphere really is thinner for them - it's not an illusion or a mathematical convenience to explain an "underlying" physical reality where the lengths and times don't change. Such a "reality" doesn't exist. Tevildo (talk) 23:09, 1 November 2013 (UTC)[reply]
Yes that about sums up the relativistic perspectives. Classically though, simultaneity is invariant and distances between spacial points don't change either. This classical paradigm actually has nothing to say about whether or not clock rates slow down or speed up due to acceleration, so your last point regarding an absolute time being nonexistent is inapplicable. With such critiques, one must be very careful to distinguish between reality and the model of reality. The latter merely needs to be self-consistent even if not true. -Modocc (talk) 00:38, 2 November 2013 (UTC)[reply]
Ironically, Galileo had a classical foundation, whereas the people he said it to whom unsuccessfully censored him were indoctrinated. Hopefully, we are a tad more civilized now, I hope, 'cause sometimes the best knowledge which is grand is hard to come by. --Modocc (talk) 20:43, 1 November 2013 (UTC)[reply]
Regarding this exchange:
Tevildo:
‘So, is there a "real diameter", which is not the difference between two sets of coordinates? If so, how is it defined? How can it be measured?”
Trovatore:
‘I didn't say there was a "real diameter". If there is no "real diameter", then there's also no "real shrinkage"...
The proper length as measured from at rest with an object, “hands on,” measuring rod applied directly to the object will be its true physical length without any complications associated with images of the object traveling at light speed meeting an observer approaching the object and its image at near light speed. The Lorentz transformation does a good mathematical job of translating the contracted images into the true, “proper,” at rest length of the object, without measurement distortion via relativistic effects. Even thought this is a criticism of SR interpretation, it does not negate the constant speed of light. That constant does not require physical shrinkage.
Yet the basic philosophy is ignored. Is Earth a “real physical object,” (independent of observation.) That question may be too philosophical for relativity idealists who implicitly philosophically (consciously or not) negate a real world independent of observation? But Earth still doesn't physically shrink, regardless of how distorted it might look from a great variety of relativistic frames. (Realism.) — Preceding unsigned comment added by LCcritic (talk • (edit) Sorry, forgot to sign. LCcritic (talk) 00:42, 2 November 2013 (UTC) contribs) 00:38, 2 November 2013 (UTC)[reply]
There's a very good book called "Boojums All the Way Down" by David Mermin which addresses the metaphysical implications of special relativity, and which I would recommend to anyone interested in the issue. The main disagreement that we (and received scientific opinion) have with your views is that you distinguish between the "true length of the object" (as measured by the stationary observer) and the "measurement distortion" of the moving observer. Both lengths are equally real/valid/true in their corresponding reference frames, despite their being different. The Earth doesn't just _look_ smaller, it _actually is_ smaller for the moving observer. The problem is (as I see it) in the meaning of the words "smaller" and "length", rather than in physical reality. It may be "intuitively obvious" that the length of an object is constant if the object doesn't change, but this intuition is invalidated by the experimental results, in the same way that a stationary Earth and moving Sun is obvious but invalid. Tevildo (talk) 01:12, 2 November 2013 (UTC)[reply]
The answer is "Yes, but you're measuring it wrong." SR is special cases. The implications of SR and more fundamentally, "non-zero mass" frames of reference and general relativity, affect all observable phenomena because our common experience uses inappropriate measures. Just like I can create a model that says the sun rotates around the earth in 24 hours, rather than the earth rotates around the sun in 365 days, doesn't have any implication on what the earth or sun is. We can create earth centric frames and describe mathematically what everything looks like and indeed we do. "The sun is directly overhead", "Sunrise is at 7:00 a.m", "London is 5 hours ahead of New York", are all terms you can relate to but in no way represent the physical nature of what is observed. --DHeyward (talk) 11:03, 2 November 2013 (UTC)[reply]
Observations such as "The sun is directly overhead" are entirely valid measurements though, but there is certainly a tendency for us mere mortals to incorrectly model our measurements. The adage garbage in garbage out tends to apply to beliefs not observations (although witnesses can be unreliable). Presently, there are umpteenth interpretations of quantum mechanics and these cannot all be correct. With my doorframe experiment, the students' heights will depend on the time of year due to changes in humidity, but the students do not have different intrinsic heights because of this effect. Yet if my doorframe was a part of the royal standards two thousand years ago and the castle's witch was unaware of its varied moisture content she might have insisted that the subjects' time-dependent heights were a reality and without an alternative explanation for her observations her subjects would have likely have believed her too. Modocc (talk) 14:32, 2 November 2013 (UTC)[reply]
SR is nonEuclidean [pseudo-Euclidean] which means that the weirdness is inherent in the model, thus it cannot be interpreted as simply as a way of transforming images that are convenient to one's reference frame. In other words, either its postulates are valid or they are not because there exists an alternative model that is less weird [2]. -Modocc (talk) 15:37, 2 November 2013 (UTC)[reply]
OK, this is the second time I've had to correct this. Please stop calling SR "non-Euclidean". SR applies in flat spacetime, so it's as Euclidean as it gets in this context. GR is non-Euclidean. --Trovatore (talk) 02:37, 3 November 2013 (UTC)[reply]
I struck that. What I was trying to say was that SR is not Galilean relativity, which will preserve the Euclidean geometry of spacial distances, such that cubes remain cubes independent of reference frame. In other words, if spacial distances are absolute, then there exists a model of that space and it's not SR. -Modocc (talk) 09:05, 3 November 2013 (UTC)[reply]
Pseudo-Euclidean is, as I said, as Euclidean as it gets in this context. So calling it "non-Euclidean" is confusing and inappropriate. --Trovatore (talk) 19:10, 3 November 2013 (UTC)[reply]
For simplicity sake I'll let Tevildo's statement serve as an example for all cases of supposed contraction: "The Earth doesn't just _look_ smaller, it _actually is_ smaller for the moving observer." This (perhaps unconsciously) endorses idealism (There is no world independent of observation) and negates realism (The world's physical properties do not change with how you look at them.) He does not differentiate between Planet Earth as is (and as it was before observers evolved)... as it has been for billions of years (though slowly getting fatter around the equator)... and how it might look from a relativistic perspective "for a moving observer."
So it's polar diameter "IS" 4000 miles "for" my ship approaching at .866c from the axis direction (and its equatorial diameter IS 7926 miles.) Then the ship turns around and approaches at 90 degrees from the axis and, whaddaya know, now the equatorial diameter "IS" 4000 miles and the polar diameter IS 7901 miles. Please just explain that if you can, Tevildo. Please include the physics of such 'massive' planetary shrinkage, restoration/expansion and then more shrinkage in the opposite direction. Then please explain how the phrase "for a muon" makes the atmosphere shrink to way less than 1000 km (as well established by science) in front of each muon. Then please explain how the distances between stars (as naturally distributed in space) "IS" contracted by relativistic interstellar travel. Thanks. LCcritic (talk) 18:31, 2 November 2013 (UTC)[reply]
Lorentz transform covers the mathematics. These equations are consistent with experimental results and therefore are the basis for the theory of relativity, in the same way that F = GMm/r2 is the basis for Newton's theory of gravity. The universe happens to behave in that way. _Why_ it does is a metaphysical question - science (attempts to) describe _what_ the universe does, and what it does is follow the Lorentz equations. That being said, purely in the realm of metaphysics, philosophical realism does _not_ state "the world's physical properties do not change with how you look at them" - it states that the world exists independently of observation, but only that it _exists_, not that its properties have to behave in any particular way. Tevildo (talk) 18:52, 2 November 2013 (UTC)[reply]
Sounds like folks here are hung on semantics. When we refer to the "mass" of a particle, we generally mean "rest mass". So when we speak of the "width" of a ladder, should we not imply "rest width"? The ladder doesn't shrink - its "relativistic width" is just different. Wnt (talk) 19:12, 3 November 2013 (UTC)[reply]
Tevildo, you have totally avoided every point in my last post. If you say that the math proves length contraction (say, because it is the reciprocal of time dilation) then, for instance, a slow ticking clock on a fast moving interstellar ship is supposed (theoretically) to make the distance between stars contract. Given that the stars are distributed in space independently of how distances might be observed by fast ships, or how slowly their clocks might keep time at high velocity travel, the claim that stars move closer together "for" all such (futuristic) ships... the faster the ship, the closer the stars to each other... is very foolish and obviously false. That is the argument from realism as opposed to the idealism, which claims that there is no real, actual distribution of stars in space (or diameter of Earth) independent of how variously such distances might be seen as above.
Nor did you address the infinite variety of Earth diameters as measured from all possible frames traveling at all possible speeds and approaching from all possible directions. Again, the (perhaps unconscious) philosophical assumption is, "There is no real world (Earth) independent of observation." Your claim (often used by SR theorists) that, "These equations are consistent with experimental results" *does not address my challenge*, either in my original post or my last one. It is not "metaphysics" to "disambiguate" length contraction as above. It is, in fact, *metaphysics* to claim an infinite number of Earth diameters (in all possible directions) without a shred of *physics* to support the claim. The claim that the world changes as measurements of it change (relativistically speaking) IS metaphysics, meaning beyond physics (in the realm of idealism). Please address the points as I made them. If that is too much to ask, then please just answer the one question addressed to you above: [So it's polar diameter "IS" 4000 miles "for" my ship approaching at .866c from the axis direction (and its equatorial diameter IS 7926 miles.) Then the ship turns around and approaches at 90 degrees from the axis and, whaddaya know, now the equatorial diameter "IS" 4000 miles and the polar diameter IS 7901 miles. ** Please just explain that if you can, Tevildo.**] LCcritic (talk) 19:08, 3 November 2013 (UTC)[reply]
There are few responses that can be made to the argumentum ad lapidem, and I doubt if I can find one here. Your statement "the faster the ship, the closer the stars to each other is very foolish and obviously false" is a perfect example of an ad lapidem - all I can do is repeat my statement that it isn't consistent with physical reality. If you go through the mathematics in Lorentz transform, Derivations of the Lorentz transformations, and the (IMO, rather more accessible) derivation in Mermin's book, you'll see how the equations are derived from first principles, as a general statement of how measurements in two different frames, moving with respect to each other, are related. These equations involve the invariant velocity, c, which, by combining the Lorentz transform with Maxwell's Equations, can be demonstrated to be the speed of light. Because, in our particular universe, c has a finite value, which we can measure, we can therefore calculate the length contraction appropriate to the two frames you mention. Why c has that particular value may, one day, be explained by a scientific theory, but that theory has not yet been developed. Why algebraic equations can be used to describe accurately the behaviour of the universe is a metaphysical (or sociological?) question that I can't answer. I assume that you won't consider this to be an "explanation", unfortunately. Perhaps someone else may be able to provide one that's acceptable to you, but I consider it unlikely. Tevildo (talk) 20:49, 3 November 2013 (UTC)[reply]
Tevildo, I have repeatedly asked this "encyclopedia reference desk" to clarify the standard SR claim that physical objects and the distances between them contract, based on different frames of reference measuring the same object or distance differently, as if it is a given that different measurements equate to different physical lengths. My primary example has been the claim of a changing shape of Earth (with all varieties of different diameters), varying drastically with different observations from relativistic frames. The alternative "explanation" given has been that it doesn't change but *IS all different shapes at the same time*, just "depending on how you look at it" with no objective measurement of the physical body Earth possible ("all frames being equally valid."
(The following was deleted when I posted my reply... Here it is again:
You continue to evade the challenge, now citing "argumentum ad lapidem"... a logical fallacy that consists in dismissing a statement as absurd without giving proof of its absurdity." The burden of proof that Earth's shape changes, or that it has an infinite variety of shapes ("for" all possible observing frames) is on the theorists who make that claim. *There is no empirical evidence for length contraction.* The "length contraction" section should at least mention this fact, but the editors will not allow it. (I've tried.) Instead we have folks such as yourself (assumed to be experts) denying the absurdity of an earth changing shapes or having multiple shapes. Will someone here *please* address the specifics of my opening post and my last post to Tevildo, who refuses to answer my direct questions. LCcritic (talk) 18:31, 4 November 2013 (UTC)[reply]
I may regret this, but could you please state your "direct question" in one sentence without becoming abusive, so that I may attempt to answer it? I do not promise to succeed in answering it, of course, but it isn't clear to me how I have failed to answer it, as I don't know precisely what it was. And you _have_ dismissed the theory of relativity as absurd ("very foolish and obviously false") without providing an argument to support your position. This question will scroll off the desk in a couple of hours, so this will probably be our last exchange. Tevildo (talk) 22:22, 4 November 2013 (UTC)[reply]
SSRI/SSNRI WITHDRAWAL
Can someone please add SAVELLA (Milnacipran) withdrawals in with the other SSRI/SSNRI Withdrawal symptoms? It is a fairly new medication, though it has severe withdrawal symptoms, very similar to others you have listed on the page. I would just like others to be informed about coming off this medication.
I assume you want the article SSRI discontinuation syndrome changed. Milnacipram withdrawal has been studied [3] but doesn't sound impressive. A review financed by Eli Lilly and a bunch of other drug companies [4] says on page 8 that:
"A post hoc analysis of patients abruptly withdrawn from paroxetine or milnacipran as part of a double-blind comparative study showed that paroxetine produced significantly more discontinuation emergent adverse events than milnacipran. In addition, the nature of the adverse events differed between the two antidepressants, with patients withdrawn from paroxetine showing the classical symptoms of dizziness, anxiety, and sleep disturbance (insomnia and nightmares), while those withdrawn from milnacipran showed only increased anxiety. However, some discontinuation symptoms have been reported, and good clinical practice and regulatory authorities always recommend gradual discontinuation from any psychotropic drug."
Honestly, given the spotted history of drugs that have been claimed to lack their predecessors' side effects, I am skeptical to read a statement like this, but I have zero experience in this area and I'm in no position to dispute their statement. Wnt (talk) 03:41, 1 November 2013 (UTC)[reply]
There could also be negative impacts on social development. For example, if they go out with unkempt clothes, hair, etc., since they can't see a stain, etc., this might make them less popular. StuRat (talk) 15:59, 2 November 2013 (UTC)[reply]
Vision problems — especially if they are undiagnosed — can have a severe effect on educational development see:[5] Also, children who can't see well enough to play games or take part in other activities with their peers are going to miss out on social development. Richerman(talk)09:29, 3 November 2013 (UTC)[reply]
Anyone who has worn glasses in childhood has probably copped being called four eyes, which may have an adverse effect on some. If their eyes are particularly bad requiring extra thick lenses then they may receive an unusually high level of harassment. If socialising, or learning how to do so effectively is a life-skill then some children may withdraw or become anti-social because they are 'different' or made to feel different by uncaring classmates. Richermans point about undiagnosed sight problems, and the other issue of sports is a very good example. 220ofBorg12:22, 3 November 2013 (UTC)[reply]
hi, why are certain space objects moving so fast in space, while most just float?
You're probably thinking that things float in orbit. They don't. They're actually zipping along pretty quickly. For example, the International Space Station (according to the infobox anyway) is going 27,600 km/h or 17,100 mph around the Earth. It's just that there's not a lot that is stationary up there to give you visual cues.
The orbital speed of a an object orbiting Earth depends on the radius of its orbit and its eccentricity. The closer to Earth an object orbits the faster it must be going to stay in orbit. Objects in eccentric orbits speed up as they approach Earth and slow down as they move away. SpinningSpark09:59, 1 November 2013 (UTC)[reply]
i was talking about space debris. In "gravity" movie, when many things float here and there, debris come in great speed. Is that because they are propelled or some objects travel in that speed in space. Not about orbiting, about some moving randomly. — Preceding unsigned comment added by 122.164.80.142 (talk) 13:39, 1 November 2013 (UTC)[reply]
Objects in orbit are subject to the earth's gravity at a fairly significant fraction to what you are. That is, the gravitational forces on you if you were, say, on the International Space Station would not be significantly lower than what it is where you are sitting now. So why do objects float along side of you when you let go? For the same reason they would if you jumped out of a plane. Imagine, if you will, that you jump out of a plane. Now, imagine you're holding a pen when you do so. While you're faling towards the earth, let go of the pen. Will the pen go rushing towards the earth as soon as you let go? Well, not any faster than you already are. That is, the pen is already being pulled towards the earth along with you before you let it go, so when you let it go, it keeps the same motion as it already had. When you look at the pen, it appears to float right next to you, but of course, it's rushing towards the ground along side of you, just as you are. Orbit works the same way, except you have enough tangental velocity relative to the earth to avoid hitting it. That is, you're essentially falling in a circle and missing the earth on every pass. If you let go of your pen in orbit, it floats along side of you for the same reason it did when you jumped out of the plane. Because you were both moving together before you let it go, and nothing changed about the forces acting on it and on you when you let it go. --Jayron3214:43, 1 November 2013 (UTC)[reply]
Adding to that, if something is moving fast relative to something else in space (that is, not floating along with it), it is because it is on a significantly different orbit. I haven't seen Gravity, so I don't know the context for the fast moving objects, but things with intersecting orbits can pass each other VERY quickly. 2009 satellite collision is a recent example of a collision. They collided at 26,000 mph. Katie R (talk) 14:53, 1 November 2013 (UTC)[reply]
BTW, the perpetually falling aspect is the same feeling as real falling whence the large rate of nausea for astronauts and the vomit comet training. The tangential velocity keeps you from hitting but doesn't offset the feeling. --DHeyward (talk) 09:47, 3 November 2013 (UTC)[reply]
They do indeed evolve, but the nature of their evolution is a bit different. When lifeforms evolve, they generally don't have a lot of "unused circuitry" to draw on; typically genes that are unused are quickly lost in the course of evolution. But cancer cells have many more genes and developmental programs to draw upon than what they should be using, because they are differentiated and, typically, want to become dedifferentiated, calling on abilities from other tissues such as the ability to degrade extracellular matrix with matrix metalloproteinases, turn on telomerase, and of course to undergo rapid cell cycling and growth with oncogenes. Wnt (talk) 07:14, 1 November 2013 (UTC)[reply]
This is the second time you have asked this exact same question - you asked it here on 23 October. It attracted sevearal good answers. What was wrong with them? — Preceding unsigned comment added by 120.145.135.143 (talk) 07:17, 1 November 2013 (UTC)[reply]
thanks for assisting. Last time, my question was deleted immediately wanting to discuss such things in an outside forum. I was not aware that it was reactivated. — Preceding unsigned comment added by 122.164.80.142 (talk) 13:35, 1 November 2013 (UTC)[reply]
Because Apollo 13 followed the free-return trajectory, its altitude over the lunar far side was approximately 100 km greater than the orbital altitude on the remaining Apollo lunar missions. Due to this fact, Apollo 13 holds the absolute altitude record for a manned spacecraft, reaching a distance of 400,171 kilometers from Earth on 7:21 pm EST, April 14, 1970.
Apollo 8 entered moon orbit. Apollo 13 only uses moon to capture them and sent them home.
Is it a good idea to say that merely 100 km farther away from the dark side of the moon than previous missions could earn them this world record? -- Toytoy (talk) 11:18, 1 November 2013 (UTC)[reply]
Good spot, that's somewhat misleading (it beats Apollo 8 by about 2,800km, not 100km). It was not that they were further from the moon which gained them the record, it was that they were futher from the Earth (and, as it happened, the moon was further from Perigee than during other missions) The fact is cited to Guiness World Records 2010, so I can't be sure if the inference is theirs or not. I don't seem to be able to find it on the GWR website. Either way, it should be changed to remove the misleading "due to this fact". MChesterMC (talk) 13:44, 1 November 2013 (UTC)[reply]
Specifically, from Copper : "Together with caesium and gold (both yellow), and osmium (bluish), copper is one of only four elemental metals with a natural color other than gray or silver.[8] Pure copper is orange-red and acquires a reddish tarnish when exposed to air. The characteristic color of copper results from the electronic transitions between the filled 3d and half-empty 4s atomic shells – the energy difference between these shells is such that it corresponds to orange light. The same mechanism accounts for the yellow color of gold and caesium." loupgarous (talk) 00:12, 2 November 2013 (UTC)[reply]
Greatest and Least Surface gravity on inhabitable planet?
Assume a planet with a core and mantle somewhat similar to Earth or one of the other inner planets. What is the Greatest and Least possible *surface* gravity for a planet that Human beings and Earth plants would be otherwise be able to inhabit? I'm wondering because if the planet is much larger than earth then it would seem to be likely to keep it's Hydrogen in a way that would make the planet otherwise unusable and if it was much lower, then the Oxygen would be able to escape relatively quickly in the planet's life. (See Mars, which would be worse if it were closer, I think.)Naraht (talk) 15:17, 1 November 2013 (UTC)[reply]
You must take air temperature into consideration.
If the planet is hot (but not too hot to boil living things), then gas molecules would be more likely escape from it.
If the planet is cold (but not too cold), then gas molecules would be less likely escape from it.
The air temperature is determined by TOO MANY factors other than surface gravity:
It may be affected by: the planet's rotational axis, the sun's strength, the distance between the planet and the sun, whether it has a moon or moons, the color of the ground, the existence of sea and the composition of the sea (salinity and color), mountain ranges, the air's color (see Jupiter), greenhouse gases ...... blah blah ...... -- Toytoy (talk) 15:31, 1 November 2013 (UTC)[reply]
I agree that temperature would need to be taken into account. However the specifications for survival of both Humans *and Earth Plants* would keep the temperature within a *relatively* narrow range. (Assume on one end for temperature a strip with weather no worse than Calgary along the Equator and on the other with Poles no warmer than Jakarta). The Star would also have to generate enough energy in wavelengths that Earth plants could use to survive. (Let's say F, G, or K class, though that may be too broad).Naraht (talk) 15:43, 1 November 2013 (UTC)[reply]
Surface gravity per se is probably not the dominant factor. For example, Saturn actually has a lower surface gravity than Earth (about 90%, because of its very low density). However, the rate of decrease in gravity with altitude is far slower than on Earth, so Saturn is much better at holding on to its atmosphere. Looie496 (talk) 16:04, 1 November 2013 (UTC)[reply]
Saturn is the first thing that came to mind, but if we assume your ecosystem needs ground to stand on (otherwise, Venus is nearly habitable, except for the nasty sulfur making its clouds acid instead of water). So for the largest planet, we're basically supposing it has density of 1 g/cc all the way down to the core, so you can stand on the surface. (The planet could be made out of any number of things, but for purposes of discussion I'll say "turtles".) That means the planet has mass M = 1 g/cm3 r^3, where r is your distance from the center. Mass of Earth is 6 x 1027 g and its radius is 6.36 x 108 cm. For Earth mass of our light planet, you have radius 1.8 x 109 cm (cube root of the volume), which is 2.9 times further, which means you'd actually have only 1/8 the gravity! Yet we know full well the gravity well is as deep, so gas molecules at the top of the atmosphere would need the same escape velocity, and so the planet would lose atmosphere at the same rate as Earth... wait, erm, no, because the top of the atmosphere is so much bigger, it would lose it 8x faster. But then again, it would probably have 24x the gas to start with inside of it. But how much reaches the surface? Hrm, the ugly head of reality noses unwanted into the tent. But gas release ought to be at least 8x more, so surface gravity could be 1/8 Earth's with the same atmosphere. oops, wait, it's just as deep at the center of the planet, but ... The scale height of the atmosphere will be a little teeny bit different, but not much - Earth's atmosphere is so thin that the difference in gravity between top and bottom is miniscule, and for the bigger planet it is even less. Wnt (talk) 16:37, 1 November 2013 (UTC)[reply]
But you have a relatively narrow line to walk between losing Hydrogen fast enough and not losing Oxygen. If the functional atmosphere is that much be that much bigger won't it lose Oxygen faster as well?Naraht (talk) 16:46, 1 November 2013 (UTC)[reply]
Erm, I might have gone "out of my depth" on this one. Every time I think about it there's some factor I forgot about that throws the whole result off by a factor of 3. Wnt (talk) 17:03, 1 November 2013 (UTC)[reply]
The ability of the planet to retain hydrogen and oxygen really isn't much to do with gravity. Both hydrogen and oxygen are highly reactive elements and won't remain in the atmosphere as gasses for very long. On earth and other planets that we can study easily, the oxygen reacts with elements such as carbon, iron and hydrogen to make CO2, rust and water - and hydrogen reacts to make methane, water and such like. There may once have been free oxygen on Mars - but it's long been combined with the iron and carbon in the crust - which is why Mars is such a pretty shade of red and has a CO2 atmosphere. There would be no oxygen in the air here on Earth if it were not for plants doing photosynthesis to continually regenerate it - and there isn't much hydrogen in our atmosphere because it reacts with the oxygen too easily.
Obviously if a planet's gravity is too low, then it won't be able to retain any useful amount of atmosphere at all - and the threshold for that is somewhere between Mars (which has an atmosphere) and our moon (which has a very tenuous one).
But as others have pointed out - it's not all about mass and gravity. Look at Venus, its mass and surface gravity are a little less than ours yet it has an atmospheric pressure about 100 times greater than Earth. Divers can survive for long periods at up to 7 times atmospheric pressure providing they breathe the right mix of gasses and decompress slowly enough when they return...but above that is dangerous. So Venus is an example of a near-1g world that has way too much atmosphere.
As to the survivability of humans, it's clear that we do very badly in zero-g - astronauts who spend more than a few months in space suffer all sorts of dangerous and sometimes irreversible changes. There have been no experiments testing the lower limit however. It's difficult to produce g-forces other than 0g or 1g - and the length of time astronauts spent on the moon wasn't enough to really understand the effects of 1/6th g. Presumably there is a lower level of gravity that's tolerable - but we simply don't know what that is. For higher than 1g, we know that an average person can only tolerate 4 to 6 g for short periods without blacking out - and even that is only tolerable for a few minutes. But again, it's hard to maintain a continuous g-force of more than 1g - so we really don't know what would happen if someone were to live at 2g for a year. We really only know that humans need more than zero-g and less than 4g - but whether the practical long-term limit is 0.5g to 2.0g - or 0.9g to 1.1g - or 0.1g to 2.0g...we really have no idea.
SteveBaker, You might want to revisit your claims about hydrogen and oxygen. Oxygen occurs in the atmosphere in significant quantities in gaseous form in direct contradiction of your statement, and as I understand it, even with the high levels of oxygen, which rapidly oxidises hydrogen, ongoing dissociation of water due to solar radiation still results in a steady loss of hydrogen to space as a result of the low atomic weight. — Quondum16:55, 2 November 2013 (UTC)[reply]
How Can the Most Distant Galaxy be 30 Billion ly away when the universe is only 13 Billion ly old?
I can't wrap my head around it. Recently, a most distant galaxy was discovered and its distance given as 30 billion light years from earth. Given that the universe in "only" 13.8 billion light years old, and doesn't expand faster than light speed, how is that possible? (The article also mentions "another" distance as 13.1 billion light years. So what are these two distances?) Even if space has expanded, wouldn't it have expanded at the same rate, i. e. having a maximum radius of 13.8 billion ly? You couldn't fit 30 billion light years in that... Help, please?! -- megA (talk) 22:06, 1 November 2013 (UTC)[reply]
Space can expand faster than light. The lead of your linked article Z8 GND 5296 has a link on expansion of the universe which says: "While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, it places no theoretical constraint on changes to the scale of space itself." PrimeHunter (talk) 22:28, 1 November 2013 (UTC)[reply]
Yup, that can happen. The schoolbook analogy is a snail crawling on a rubber band. The snail can only crawl at some maximum speed but that speed is independent of and places no limit on how fast you can stretch the rubber band. 88.112.41.6 (talk) 23:15, 1 November 2013 (UTC)[reply]
Especially that damned inflation. Only I wouldn't characterize it as "dragged". The expansion is AFAIK in all directions, not just one. When a balloon is inflated, you wouldn't say a spot on it was dragged. Clarityfiend (talk) 23:35, 1 November 2013 (UTC)[reply]
To say "space expands faster than light" is a confusing (and inappropriate) way to describe it; a better way of saying it is that the total distance between two particular points can increase at more than the speed of light due to the expansion of space, if the points are far enough apart. A nice way pf thinking of it is that the path that the photon from the galaxy traveled in the past got stretched in the time since it went past, but this stretched path length is what we mean when we determine the (current) distance to the galaxy, which is inherently longer than the distance traveled by the photon. — Quondum00:30, 2 November 2013 (UTC)[reply]
There's something innately confusing about that description, because it describes a spacelike interval between two galaxies that are a long way away from one another. The article even says it is beyond the cosmic horizon - does that mean that light from it "now" (whatever "now" involves it 30 billion ly away...) will never reach us? If so, I'm really curious to hear just what frame of reference this distance is measured in... Wnt (talk) 01:00, 2 November 2013 (UTC)[reply]
The universe is changing over time. For example, the CMBR temperature is currently about 2.7 K. "Now" in a distant galaxy is whenever the CMBR temperature measured there is 2.7 K. The distance "now" to that galaxy is the minimum, over all chains of galaxies connecting it to ours, of the sum of the distances between consecutive galaxies in that chain, measured in the local frame where the CMBR is isotropic. There are other ways to define it, of course. The important thing is that the Big Bang breaks the symmetry of reference frames.
I'm not sure what it means to say that it's beyond the cosmic horizon, but probably it does mean that light emitted "now" will never reach us. The cutoff distance for that is , where a(t) is the function given here. I can't remember what that evaluates to but it's more than 18 billion light years and likely less than 28. -- BenRG (talk) 05:45, 2 November 2013 (UTC)[reply]
A dumbed down Kindergarten level explanation. Let's take the balloon model as explained above by the IP and others. Then the rate at which two points are receding will be proportional to the distance (if every meter is expanding and becoming larger at some rate then if you have twice as many meters between two points, so the distance must grow at twice the rate). So, you then have Hubble's law that says that the speed v between distant galaxies is v = H d, where d is the distance and H the Hubble constant. If we ignore the new results about the acceleration of the expansion rate due to dark energy and simply consider H to be constant, then that is good enough to roughly understand the two numbers 13.1 billion light years and 30 billion light years.
Then consider what happens when we observe distant galaxies. You don't see them as they are now, rather, you see them as they were when the light left the galaxy. If you measure the distance what you get is not the distance they are from us today, rather you get the distance from us to the point where they were when the light left the galaxy. The Hubble law v = H d based on these distance and speed measurements relates the distance in this sense to the velocity. The farthest you can see in theory is that distance where the velocity would be the speed of light.
So H = c/(13.8 billion light years) = 1/(13.8 billion years).
Then we can ask how far away would a galaxy be from us today if d = 13.1 billion lightyears. If the distance at time t is x(t), then the speed is the derivative dx/dt and this must equal H x by the Hubble law, so you have dx/dt = H x. This is a differential equation with the solution
x(t) = x(0) exp(H t) = x(0) exp[t/(13.8 billion years)]. Then for the galaxy we can take t = 0 the moment when it was at the point where we observe it now. That point is 13.1 billion light years away, so x(0) = 13.1 billion light years. The distance today is then found by taking t = 13.1 billion years, this gives x(13.1 billion years) = 33.8 billion light years. So, this dumbed down model is quite accurate. Count Iblis (talk) 01:21, 2 November 2013 (UTC)[reply]
Well, it's an interesting way to calculate things. For example, consider a soda can that has fallen into a black hole and is about to hit the singularity. You track back to a time when it had an observed distance to a spaceship it was tossed out of, track the relative rates of separation, get a distance... But it's not a distance the can can travel to get anywhere. Depending on what frame you looked at them in when they were close together, the distance between them could have been foreshortened to any degree from nothing to practically 100%, yet you could still be in the black hole next to the tin can. Wnt (talk) 04:51, 2 November 2013 (UTC)[reply]
I made this picture years ago. It's an illustration of the shape of the expanding universe (earlier times at the bottom), based on cosmological parameters measured by WMAP. The yellow line on the right is a distant object, the brown line on the left is us, the diagonal red line is light from the distant object to us, and the orange line at the top is the separation "now" between us and the distant object. Each grid rectangle is 1 billion years by 1 billion present-day light years. You can check by counting grid rectangles that the object is 28 billion light years away "now" and the light was emitted 12 billion years ago. The light always travels at a 45° angle to the grid lines. -- BenRG (talk) 05:09, 2 November 2013 (UTC)[reply]
Thank you very much, BenRG, that picture really makes it clear how these two figures are to be understood. So, to sum it up, the light emitted from "that galaxy" has traveled for 13 million years, but the space it has already traveled through has expanded in the meanwhile, namely to 30 million light years. Ahh, sweet Epiphany! -- megA (talk) 11:11, 2 November 2013 (UTC)[reply]
Could there be an error in the phrasing of the original question? A light year is a measure of distance, not time. So to say that "the universe [is] 'only' 13.8 billion light years old" is incorrect. Perhaps the OP meant something different and everyone else (but me) understood anyway. El duderino(abides)06:15, 5 November 2013 (UTC)[reply]
November 2
Is it easy to separate individual voices from a crowd chatter?
If they're all equidistant from the microphone and all talking at once in roughly the same volume, it would be very hard to do. Maybe only if you could isolate a narrow pitch range and filter out the others. Everyone knows what a murmuring crowd sounds like, but it's hard to quantify it. One trick I've heard of is when making a film with a scene requiring background crowd murmur, the extras are advised to say "rhubarb" over and over, and obviously not in sync with each other. ←Baseball BugsWhat's up, Doc?carrots→ 12:10, 2 November 2013 (UTC)[reply]
Separating mixed up voices from a crowd electronically is extremely difficult (see Source separation). You can use a highly directional microphone to record only one person at a time. You could also record the crowd with multiple microphones and maybe use software to correlate sound coming from different places in the audio field - that can work reasonably well...for example, one simple trick for removing the vocals in a stereo music recording is to eliminate any sound that appears in both channels (by subtracting one from the other). Since most recordings place the singer in the center of the stereo image and all of the instruments off to the sides, the result is a monophonic recording without the vocals.
Interestingly, humans are very good at doing this - it's called "The Cocktail party effect" - and we have an article about that. You might also read Selective auditory attention and Auditory scene analysis. In part that's because we have two ears and all of those wrinkles in the ear and can process things like the phase shift of sound as it passes through the skull...with those tools, we can accurately locate a sound in three-dimensional space and turn our heads towards it with fairly high precision. That helps to narrow down the voice that we're interested in - but even so, the auditory processing that goes on in our heads is highly sophisticated and beyond what we can currently achieve with electronics and software processing.
Note, though, that one of the first signs of hearing loss is the inability to pick specific voices out of a crowd. However, I'm not sure if this is a result of damage to the ear itself, or the post-processing which occurs in the brain to make this determination. StuRat (talk) 15:28, 2 November 2013 (UTC)[reply]
I was almost deaf in one ear (with near-perfect hearing in the other) for about a year before I got treated for it - and I can confirm that loss of hearing in one ear makes it almost impossible to separate out even two people talking at once - I'd have to turn off TV and music if I wanted to have a reasonable conversation. That was purely an inner ear issue - so loss of post-processing capability in the brain wasn't the cause. SteveBaker (talk) 15:53, 2 November 2013 (UTC)[reply]
Hmm, maybe I should get my hearing checked out. I have always found it difficult to pick up individual voices in a louder crowd - one of the main reasons I have always disliked noisy clubs and bars. I find that unless I consciously make the effort to filter what I am listening to (which is quite tiring) my auditory focus drifts involuntarily between different conversations going on around me and I often lose half a sentence of what someone is saying. Also, I hate having a conversation with a TV on in the background, although that's probably more because I am old-fashioned and feel that the person I am having a conversation with should both get and give undivided attention. Anyway, that's a rambling way of saying thanks for the heads up - I'd always considered this within the range of "normal", and now I might actually go and get it looked at by a medical professional. Equisetum (talk | contributions) 18:10, 2 November 2013 (UTC)[reply]
I don't want to get into the realms of medical advice, but I have excellent hearing (in terms of being able to detect sounds), but still suffer from the same problem. Perhaps we should both see psychiatrists rather than audiologists. Tevildo (talk) 21:45, 2 November 2013 (UTC)[reply]
If you have as many microphones as there are speakers, and if the microphones are scattered around so that each microphone hears an independent linear combination of the voice signals (being different distances from each speaker), then theoretically it should be possible to invert the matrix of linear combinations and obtain each of the voices as a separate signal. If you have different numbers of speakers and microphones, then singular value decomposition is needed. This is the basis of MIMO (using radio rather than sound propagation), and is why your wireless router sports more than one antenna (multipath propagation due to reflection from walls and objects in your house should ensure that the amplitude and phase at each antenna is uncorrelated even though the antennas are only of the order of a wavelength apart). --catslash (talk) 18:17, 2 November 2013 (UTC)[reply]
Every observable corresponds to a linear operator. You can define an infinite number of operators that don't correspond to observables, aren't Hermitian, etc. For example, squaring the wavefunction is not linear. --Bowlhover (talk) 16:45, 2 November 2013 (UTC)[reply]
No you can't do that, because that's not physical.
That's like saying you can't introduce creation and annihilation operators for electrons because you can't create an electron out of the vacuum as that would violate conservation of energy and conservation of electric charge. Count Iblis (talk) 19:02, 2 November 2013 (UTC)[reply]
Yes, the time evolution operator is a linear operator and because any observation one can make is ultimately due to coupling the system with a measurement apparatus and letting that combined system evolve in time, observables must also be described by linear operators. Then while some have proposed non-linear time evolution as a mechanism to implement a real wave function collapse as opposed to an apparent one due to decoherence (linear collapse models are always mathematically identical to the system being coupled to additional degrees of freedom), they all suffer from violation of local energy and momentum conservation. So, there are good reasons to believe that time evolution and hence observables are exactly linear and not just to some good approximation as can be determined by experiment. Count Iblis (talk) 20:47, 2 November 2013 (UTC)[reply]
"In classical physics there are, of course, many examples of non-linear systems" – yes, and in quantum mechanics too. The linear operators in quantum mechanics operate on the phase space (the wave function). Classical mechanics is linear in phase space too, to the extent that it makes sense to talk about that. The more usual sense of nonlinearity in classical physics remains unchanged in quantum mechanics. The strong force is definitely not linear. -- BenRG (talk) 21:54, 2 November 2013 (UTC)[reply]
If energy is conserved, why do we run out of energy?
A car converts gasoline into kinetic energy when it starts moving. Why can the kinetic energy not be converted back into gasoline when the car comes to a stop?
It's converted into heat. Next time you go for a jog in the summertime be sure to really bundle up. Really layer it on, sweater, coat, gloves, etc. Then jog around for a few kilometers then bring all that heat energy back home and use it to boil water for your dinner. (You should have saved up enough energy to bring at least a few liters of water to the boiling point, no?)
Iblis has it, but in case the physics in that article is a little too dense, here's the "lay" version (and it's only little bit wrong, but not in any way that will screw up your understanding). The basic idea is that energy is always conserved, but entropy is not. Entropy is kinda a hard concept, but the easiest way to think of it is as energy which exists, but is unavailable to do work. As you do work, of any sort, some amount of energy you input into a system to do work is converted to heat because of friction (or some equivalent of friction in whatever system you're working in). So, energy input is always more than work output. The difference between the energy input and work output is basically entropy. The energy is there, it's just gone towards warming up the environment a bit, and not towards doing whatever useful work you were doing at the time. --Jayron3201:28, 3 November 2013 (UTC)[reply]
This is what certain models of car actually do - they don't convert the kinetic energy in to gasoline, but into electricity which is stored in batteries for future use. The Honda Insight has a system like that. --TammyMoet (talk) 20:06, 2 November 2013 (UTC)[reply]
Certainly you can use the kinetic energy to charge up a battery - you could probably use battery power to drive a chemical reaction to turn water and CO2 back into gasoline - but the amount of chemistry involved would probably be horribly complicated. The biggest problem is that driving a chemical reaction 'backwards' will be highly inefficient - so you might be collecting electricity for weeks to make a thimble-full of gasoline - and you might also need a trunk-full of chemical plant to do the work. Basically, it's theoretically possible - but in practice, no - you can't do that. What you can do (and some cars actually do do) is to store electricity from regenerative braking - and use that to accelerate the car for the first few yards of acceleration when you pull away from a standing stop. SteveBaker (talk) 03:04, 3 November 2013 (UTC)[reply]
Also, even if you could convert kinetic energy back to gasoline with 100% efficiency, you'd still need to deal with kinetic energy lost due to friction, including air resistance. StuRat (talk) 05:16, 3 November 2013 (UTC)[reply]
You can't convert it back to the gasoline that was used to accelerate the car with 100% efficiency even in theory (i.e. assuming zero friction during acceleration and some ideal braking method that converts all of the kinetic energy back to work with 100% efficiency). The reason is that that in the ideal limit of zero friction a hypothetical car engine will still not be able to use all of the Gibbs energy difference between the gasoline and the combustion products when the latter are dumped into the atmosphere.
The reverse process of bringing back the gasoline would require at least that amount of work that you could have maximally have extracted from the gasoline, which involves processes that an ideal car engine is not going to make use of. The reason is that the car engine is required to be a device that fits into the car, you will have imposed some restrictions on the size of the car and you require the engine to deliver some finite amount of power. The theoretical limit is to be understood as the best possible efficiency that the laws of physics allows you to get under such constraints. This then implies that you can't reversibly mix the exhaust gasses with the atmosphere, what comes out of the exhaust will not have the same composition as the rest of the atmosphere. The amount of work that could have been obtained by reversibly mixing the exhaust gasses with the atmosphere is thus going to be lost.
This is not a very small amount of work (although it is an order of magnitude less than the caloric value of gasoline). E.g. given a litre of water you could in theory extract enough work to lift a weight of 10 kg about 700 meters if the ambient humidity is 60%. So, in theory you can make a water pump that will get all of its required energy from reversibly evaporating 10% of the water which will be enough to pump the rest of the water almost a kilometer up a hill. Count Iblis (talk) 16:26, 3 November 2013 (UTC)[reply]
November 3
Nuclear radation concerns for Utah salt lakes
Someone said a university in Utah is studying radiation of sea salt from Utah salt lakes. I use a brand of sea salt in my cooking and wonder if there is a connection. Of course checked the manufactures web site and nothing but glowing reports there. company selling the sea salt is based in Heber, Utah, near salt lake.
99.108.30.42 (talk) 02:30, 3 November 2013 (UTC)
Fred W — Preceding unsigned comment added by 99.108.30.42 (talk) 02:16, 3 November 2013 (UTC)[reply]
I am concerned about underground nuclear tests in past which vented radioactive gases in that area and may have contaminated the sea salts. Sorry, I did not really think through my question.
108.78.185.140 (talk) 15:27, 3 November 2013 (UTC)[reply]
There are many potential reasons, because isotope analysis is a general geology technique and Utah is a site of commercial potassium extraction and other mining. Gamma ray logging apparently takes advantage of potassium's natural radioactivity, while potassium-argon dating is useful for dating deposits. From what you've said, this could be related to anything from fertilizer production to oil prospecting. Wnt (talk) 15:38, 3 November 2013 (UTC)[reply]
Also, regarding nuclear testing: (1) None of the tests were in the immediate vicinity of the Great Salt Lake; (2) All but a few nuclear tests in the Continental USA were done at the Nevada Test Site, which is pretty far away from the Great Salt Lake -- so the amount of fallout reaching the lake was small; (3) Atmospheric nuclear testing in the USA was discontinued after 1962 -- so almost all of the radiation that did reach the Great Salt Lake should have decayed by now; and (4) As for underground nuclear tests, the amount of radiation that reaches the surface is medically insignificant. 24.23.196.85 (talk) 06:35, 4 November 2013 (UTC)[reply]
Reversing batteries in compartment saves the batteries from trickle charge depletion, why?
I have reversed my batteries in old flashlights, walkmans, portable electric razors, etc. and the batteries stay fairly fresh and usuable when needed and reversed, even after six months or more. Why is that and is there any potential for using that approach in conserving energy on big scale, such as a electric power plant.
You took the batteries out and put them back in with the + and - ends reversed? Wow! Well:
For a simple incandescent bulb flashlight - this can't possibly make a difference. The only active component in the circuit is the bulb itself and it is basically just a resistor - it has the same resistance no matter whether it's driven forwards or backwards. Since V=IR (ohms law) - the current that flows depends on the resistance - I don't see how reversing the battery could possibly have any effect whatever. For a modern LED flashlight, it won't work - and you might destroy it.
For things like a Walkman - which has electronic circuits in it - you're running the risk of destroying the electronics by doing this - so I strongly advise you not to do it anymore! You're probably getting away with it because the battery is alreay depleted...but it's a really bad idea! It's also unlikely that these devices would work with the batteries reversed...so I can't believe you've actually done this.
For electric razors...simple, old-style razors are basically just DC motors. The motor would probably run backwards - which might mean it still shaves OK - but maybe not. More modern razors may have some basic electronics in them - and just like with a Walkman, you'll probably damage it.
Worse thing, the little spring that is supposed to press against the negative end of the battery can possibly short out the positive end - it's not likely - but if you do short out the battery you'll cause rapid overheating and possibly even a fire, even if the battery is towards the end of it's life.
Sorry - but this sounds like complete nonsense. Certainly we're not going to save energy by doing this - and most likely, this advice will cause people to destroy expensive electronics by attempting it.
Could there possibly be electronic circuit protections against reversed polarity which create an open circuit and thus prevent discharge ? StuRat (talk) 04:06, 3 November 2013 (UTC)[reply]
Diodes have asymmetric conductance, only allowing current to flow in one direction, so when reversed polarity current reaches a diode, it essentially creates an open circuit. This is why, as Steve mentions, LED (Light Emitting Diode) flashlights won't work with the current reversed. But everything Steve says above is correct. It isn't a good idea and may ruin more delicate circuitry. In fact, I believe the fine print on battery packages warn against it (at least in the U.S.) saying things like "fire or other injury may result".--William ThweattTalkContribs05:33, 3 November 2013 (UTC)[reply]
Yep, nobody is saying it's a good idea, but conceivable an LED flashlight, which slowly drains batteries placed in normal polarity, might not drain them in reverse polarity. StuRat (talk) 06:08, 3 November 2013 (UTC)[reply]
First time here on this and entry about salt in Utah, entered just before it. So I do not think I adequately explained myself. My uncle used to do this years ago to save on batteries. Here is what I have been doing.... I reverse the batteries when the device is not in use, then reverse the batteries for correct polarity when use is intended. I have used this on three LED flashlights and no problem. Neither a problem on walkman, razors. In fact many manufactures used to ship with batteries reversed. Now I am not saying that some circuits would not be harmed with the reversing, only that those I described were not and batteries held up much much much longer (six months to a year) than if simply left grow weak while device in "off" position.
I'd suggest that the explanation may be rather mundane: the normal cells (AA, AAA, D, C) have the + contact protruding, and the − contact flat. Battery compartments often have a recess around their contact for the cell's + contact. Reversing the cells would then break the circuit entirely, due to the geometry. This will not be the case for all battery compartments though. So check for this.
A further caution: a cell that is disconnected will self-discharge over months or years, and many cells (even sealed cells) when discharged have a tendency to leak electrolyte, which is generally highly corrosive. So storing cells in this manner is not generally advised if consequent damage must be avoided, but as a short-term storage alternative to simply switching the device off, reversing all cells (or simply the last cell) would be effective, provided that the shape of the compartment has a suitable geometry. 24.165.90.120 (talk) 17:15, 3 November 2013 (UTC)[reply]
The solution to the problem of potentially leaking acid from batteries is to store them in such a way that the electronics are above the batteries. You could also remove the batteries and store them elsewhere, but that's not so good, say, for a flashlight you might need to have immediately functional in a power failure. StuRat (talk) 17:24, 3 November 2013 (UTC)[reply]
When the user says that reversed batteries stay fresh and usable for 6 months, I say "So what?" A turned off device typically has an open circuit at the switch and no current trickling through some circuit. An alkaline battery today has a 5 year shelf life if not used (some more expensive battery types have a 10 year shelf life). So unused batteries in normal or reversed polarity in a device with an actual on-off SPST switch, at normal room temperature, should all be fresh enough for use after 10 times the stated 6 months. Storage life for a partially discharged battery is not so clear, but I still doubt a benefit from it being in a device with polarity backwards and the switch off. If current is not flowing, how does the polarity matter? Some more sophisticated gadgets powered by batteries might require some slight current to keep a clock powered, but such functions are so low current draw that a small button cell can typically keep them going for years. But if they draw some idle current and if they have a diode for reverse polarity protection, then the reversing trick might keep the batteries fresher, but at the cost of losing the clock time or the stored settings or whatever. Edison (talk) 22:36, 3 November 2013 (UTC)[reply]
But some devices which shouldn't need electricity, when not in use, nonetheless seem to slowly drain the battery when turned off. Conceivably, putting the batteries in backwards might stop that. Of course, removing them entirely should do the trick too, but that's not quite as handy. StuRat (talk) 00:19, 4 November 2013 (UTC)[reply]
So, it seems that there are several possible directions here:
Some devices will be permanently damaged by doing this (especially electronics). CONCLUSION: don't do it.
Some devices may short out a reversed battery causing rapid overheating and possible fire. CONCLUSION: don't do it.
Some devices may detect reversed batteries and protect themselves from damage, this action may well drain the battery. CONCLUSION: don't do it.
Some devices (eg incandescent flashlights) won't be affected by it...they'll function and drain the battery just the same as if the batteries were not reversed. CONCLUSION: don't do it.
Some devices may fail to make contact with a reversed battery...so reversing them does the same thing as removing them. Aside from the battery compartment being a convenient place to store batteries - there is no gain to doing this. CONCLUSION: Well, no harm, but not much gain either.
Some devices consume no power whatever when turned off - so either reversing or removing the battery has no effect. However, removing them avoids the problem that old batteries leak and reversing them does not. CONCLUSION: Remove the batteries, don't reverse them.
Some devices might consume power even when turned off (so-called "Standby Power") - and removing the batteries will definitely save energy - but at some loss of functionality due to loss of whatever function that standby power provided (eg keeping a clock running on time or providing a faster turn-on time). Reversing the battery will save just as much energy as reversing them - but all of the above caveats apply. CONCLUSION: Remove the batteries
My conclusion is that there is rarely a saving from removing the batteries from the device - and never a saving from reversing them instead. The only possible reason to reverse them is because the battery compartment is a convenient place to store the batteries. But this is a terrible habit to get into doing because of the high risk of damaging the equipment or overheating the batteries and causing an even bigger disaster. Because there is no possible gain and a ton of risk, it's a bloody stupid thing to do. There is no magical way that the life of a reversed battery can possibly be more than that of a removed battery...it's just impossible.
Personally - I think that habitually reversing batteries without knowing a hell of a lot about the device you're doing it to is an incredibly bad idea...it's not going to help and one day you're going to destroy something expensive by doing it!! If you absolutely *MUST* store batteries inside a device that slowly discharges them due to "Standby Power" - then insert a small slip of paper between the battery's positive terminal and the battery connector. In most devices, you only need to do this to one of the batteries to disconnect all of them. This will disconnect the battery and ensure that you get the most life possible.
My advice is to remove the batteries completely only if there is reason to think that standby power is a problem. That guarantees that the battery life is maximised and that battery leakage won't ruin the device. But never, ever, reverse them - that's just dumb.
I remember the Great Flood of 1993: I was a child in Ohio at the time, but every night the TV news was full of images of broken levees, flooded towns and farmland, and people stacking sandbags in tons of Upper Mississippi localities. What I don't remember was any discussion of flooding on the Lower Mississippi, and this article says the lower Mississippi basin was spared major flooding because the Ohio Valley, the Southern Plains, and basins in the southeastern U.S. did not experience the intense runoff that occurred in the Missouri River and the upper Mississippi River drainage. Why? I understand that the lower part of the river didn't get the heavy rain that occurred farther north, but the water has to go somewhere; why didn't the heavy rains from upstream cause also flooding when they flowed far downstream? Nyttend (talk) 04:16, 3 November 2013 (UTC)[reply]
I distinctly remember that flood, and while where I was living at the time wasn't decimated, I remember how bad it was. I would echo Bug's memory: the upstream rivers flooded badly but that didn't necessarily translate into downstream floods of the same proportion. Shadowjams (talk) 04:41, 3 November 2013 (UTC)[reply]
There's a whole branch of science dedicated to addressing questions like this, namely Hydrology. From what I can remember from my Civil Engineering days long ago, it involves taking into consideration things like flowrate, absorption rates of the different types of earth that make up the riverbed in various regions, etc. I don't know about the 1993 flood, but usually what prevents flooding further downstream is the preparedness of reservoirs downstream from the immediate flood area and their ability to take in the increased volume and release it fast enough yet without causing additional flooding. To oversimplify it a bit, reservoirs further down the Mississippi, where they didn't get the heavy rains, were aware that the flood waters would be coming and probably opened up their dams as much as they could to allow room for the incoming water. With each successive reservoir/dam system, the problem became less and less severe. Some other terms you might find interesting or may lead you to more links: Hydrograph, Hydrogeology, Behavioral modeling in hydrology.--William ThweattTalkContribs05:02, 3 November 2013 (UTC)[reply]
Something else to add is that successful flood control upstream often leads to flooding downstream. That is, if they were able to contain the water in the river upstream, it would then pass downstream in short order, and cause problems there. However, since they weren't able to contain the water upstream, and it flooded out over a wide area, this water did not immediately go downstream, and had time to soak into the ground, evaporate, etc. StuRat (talk) 05:09, 3 November 2013 (UTC)[reply]
Male Body Purposely Permanently Completely (As In 100.00%) Stops Producing Sperm
Is there any way that the body of a male will purposely permanently completely (as in 100.00%) stop producing sperm other than with hormone replacement therapy/a sex change? I am genuinely extremely curious about this, and Yes, this is an extremely serious question. Thank you very much. Futurist110 (talk) 05:41, 3 November 2013 (UTC)[reply]
Thanks, though azoospermia is not something which any fertile male can voluntarily get, is it (this is sort of what I was asking about in my OP here)? Futurist110 (talk) 06:11, 3 November 2013 (UTC)[reply]
Yeah, I apologize--I should have made my OP clearer earlier. Anyway, thank you very much for your link. I will make sure to check it out. I wonder if any of these contraceptives will purposely do this (what I am asking about in the OP) permanently (and/or for however long a male desires to do this). Futurist110 (talk) 06:41, 3 November 2013 (UTC)[reply]
Thanks. I already knew about castration but I forgot about it for the time being. As for a vasectomy, thank you, but I was asking specifically about the stopping of sperm production here (plus, I already knew what a vasectomy does). Futurist110 (talk) 06:11, 3 November 2013 (UTC)[reply]
I should add that such a low protein diet would have many other undesired and dangerous effects, so obviously not something to be tried. StuRat (talk) 06:25, 3 November 2013 (UTC)[reply]
For the record, in my OP here, I meant the purposeful permanent complete (as in 100.00%) stopping/halting of sperm production in male bodies using/in a way that any/every male can do this if he wanted to. Perhaps I should have been clearer about this before. Futurist110 (talk) 06:17, 3 November 2013 (UTC)[reply]
There might only be clues (see Spermatogenesis#Influencing factors), not definite answers or known solutions. All a matter of knowledge of how things work, and hacking (or rather engineering) accordingly. -- Lindberg 13:26, 3 November 2013 (UTC) — Preceding unsigned comment added by Lindberg G Williams Jr (talk • contribs)
Rubbing contact lenses
Please help me settle an argument. Many organizations, including the CDC, now suggest rubbing contact lenses with the disinfection solution prior to storage. I'm arguing with someone who thinks rubbing with saline is enough. I say that it's like washing your hands with water versus using soap. Who is right, with references if you can? Thanks. 67.243.4.94 (talk) 13:12, 3 November 2013 (UTC)[reply]
This sounds like a medical advice question to me. I think it would be appropriate for us to give sources we can find for either side of the argument, but we can't tell you who's right, which depends on a wide array of real world factors. For some people, who develop contact lens associated problems, perhaps neither was right. Wnt (talk) 15:27, 3 November 2013 (UTC)[reply]
It does to me too. That's why I didn't give a direct answer:) I expect the American academy of Ophthalmology know what they're talking about though. Of course, they always give the caveat "Follow the specific contact lens cleaning and storage guidelines from your eye care professional and the solution manufacturer". Richerman(talk)15:43, 3 November 2013 (UTC)[reply]
The advice in the link that Richerman provided generally seems good, but they left out one important fact: when washing your hands, don't use an anti-bacterial soap, because the alcohol residue in it can transfer to, and damage, the contact lenses. Instead, use something like Ivory, which does not contain alcohol. (That was the advice a few years ago, anyway.) And Wnt is right, this is ultimately a medical advice question. If you're wearing contacts, follow your eye doctor's instructions - and if anything in that link contradicts what your eye doctor said, call and ask about it. Your eyes are important, and you only get two of them, so don't screw around with them. ←Baseball BugsWhat's up, Doc?carrots→ 15:46, 3 November 2013 (UTC)[reply]
I rub my contacts with solutions as called for by manufacturers and CDC. The other person rubs them with saline before disinfecting with solutions. He doesn't, for some reason, follow their advice, but will listen to anyone or webpage, like the Cleveland Clinic, who says rubbing contacts with saline prior to disinfection is fine. 67.243.4.94 (talk) 23:45, 3 November 2013 (UTC)[reply]
Mites or similar
I need some assistance to identify some unpleasant invaders who seem to be immune to everything designed to kill creepy crawlies, short of fire. I went to use my computer at home about 2 nights ago, and found the keyboard absolutely heaving with these very small white things which look like mites - they are about the size of the non-sharpened end of a sewing pin (about 0.5mm) and very, very quick. I have so far tried washing the keyboard (it's a washable fold-up job), spraying the area with varying brands of home insecticide containing substances ranging from Permethrin to Pyrethrum with no effect. The only thing I have found that nails the little sob's is using my cigarette lighter to burn them off. Would anyone be able to give me some ideas as to what I could be dealing with please? CharlieTheCabbie (talk) 13:35, 3 November 2013 (UTC)[reply]
Seriously though, in a quick search I found some people talking about mold mites[6] - but it's really hard to identify a bug that "looks like a mite" as anything but a mite, without more data. Also, mold mites are up to 0.5 mm in length. [7]. What I'd like to know is: are the mold mites actually breeding inside the keyboard, getting out through some kind of little hole, so that your washing is useless and perhaps it has something else disgusting inside it for them to feed on? Or are they already loose in the house and swarming to the keyboard for warmth or because the smell attracts them or something? (I have no idea if they do that). You have to understand a little about where a bug comes from to get rid of it more than momentarily with an insecticide. Wnt (talk) 16:17, 3 November 2013 (UTC)[reply]
Does this "washable, fold-up keyboard" have an "inside" ? If not, then there's no way anything is inside for them to eat, so I'd guess they are eating the material the keyboard is made from itself. StuRat (talk) 16:40, 3 November 2013 (UTC)[reply]
The obvious solution is to replace the keyboard. A standard keyboard only costs about $20. You might also try putting the old keyboard in a plastic bag in the freezer. That might kill them off. StuRat (talk) 16:40, 3 November 2013 (UTC)[reply]
River chutes
Another Mississippi River question (guess where I was yesterday :-)
Note that river geography changes fairly rapidly, so those "chutes" might have contained small waterfalls, back when they were named. StuRat (talk) 18:47, 3 November 2013 (UTC)[reply]
Not particularly applicable, since these are all in flat countryside; the lowest dams and waterfalls are at St Louis, and all of these spots are well below that city. Nyttend (talk) 20:23, 3 November 2013 (UTC)[reply]
Many spices aren't very water-soluble, but are fat-soluble. Capsaicin from peppers is a prime example. Milk contains fat, unlike most beverages, so is able to dissolve the spices and carry them away from your mouth. StuRat (talk) 18:45, 3 November 2013 (UTC)[reply]
To answer the question, Newton's equation gives the _maximum_ penetration depth for the projectile. If the target is strong enough so as not to exhibit plastic deformation, or if a significant amount of energy is taken up by deformation of the projectile, the depth will be less than predicted by the equation. Tevildo (talk) 23:49, 3 November 2013 (UTC)[reply]
Let me add that the stronger the material, the faster the projectile must go before the material behaves as a fluid and the assumptions made in the impact depth formula are valid. Count Iblis (talk) 02:55, 4 November 2013 (UTC)[reply]
I suspect the underlying assumption of your Q is "Since it's dark at night, nothing can see, therefore the blind ants would suffer no disadvantage". However, nocturnal animals have eyes adapted to see in dim light, so your assumption is incorrect. StuRat (talk) 03:09, 4 November 2013 (UTC)[reply]
I guess you are referring to Dorylus. Which blind army ant species that don't forage both day and night are you referring to ? Or do you mean, why don't they only hunt at night ? I suppose a response to that might be, why should they ? I think army ants primary concerns when it comes to foraging are things like avoiding other army ant colonies, temperature/weather and food supply and they continuously adjust their foraging accordingly. The same colony may forage continuously, or only at certain times if it's too hot during the day or too cold at night for example. They're subject to predation both day and night. Sean.hoyland - talk04:25, 4 November 2013 (UTC)[reply]
(ec) Hmmm... I'm guessing you mean some species of Dorylus? It seems like people have observed them anecdotally to forage at night. [9] It's hard to research such a general characterization - best to have a specific species and locale in mind. I'd presume that the habits of army ants have a great deal to do with the temperature and related weather conditions. Wnt (talk) 04:33, 4 November 2013 (UTC)[reply]
I was watching BBC documentary about army ants. Not sure exact spice they have filmed. But they claimed that both soldiers and workers are blind. And in one episode ants came close to termite nest, but stopped their raid becose of sunset/evening, returned to temporarily nest and only reached termites next day and attacked them. Yes, I do not see disadvantages for them to hunt at night. Even more important - I do not see advantage for blind insects to hunt/raid/explore new hunting territory during day only. 67.71.98.182 (talk) 04:59, 4 November 2013 (UTC) EDIT: About temperature: documentary was filmed in what looked like jungle. And while not direct evidence of hunting only in the daylight, whole documentary was filmed in natural light setting. But again, story about attack on termites clearly stated that they stopped their raid because of nightfall. 67.71.98.182 (talk) 05:16, 4 November 2013 (UTC)[reply]
Most army ants are actually partly to exclusively nocturnal. The army ants in BBC documentary are most probably the most widely studied army ant species exhibiting nomadic raiding behavior - Eciton burchelli. And they're widely studied precisely because they primarily raid during the day in massive columns and thus are easier to observe. Though they typically still avoid direct sunlight and temperature extremes and stay beneath the shadows of heavy forest canopies or else only raid during overcast days.
The daily and seasonal "schedules" of different ant species depend largely on the conditions they have evolved to tolerate as well as their specific "niche" in the ecosystem, and they differ from species to species. The temperature ranges (as well as other factors) where they still consider it "worth it" in terms of potential loss of colony members versus the chances of finding food is usually clearly delineated. This is more generally known as the optimal foraging theory. While I can't find any specific studies on what affects raiding behavior in army ants (though there are plenty on bivouac formation), I suspect this is the reason. It's not related to the availability of light. Just ingrained instinctive behavior shaped by competition, prey and predator diel cycles and distribution, and general abiotic factors. They simply don't consider it worth it to raid beyond the specific time/condition they have adapted to. Though if they had reached the termite nest before nightfall, the attack may have occured earlier.-- OBSIDIAN†SOUL06:22, 4 November 2013 (UTC)[reply]
